The web has become a central part of our daily lives. However, the short lifespan of online data poses serious challenges for preserving and safeguarding this digital heritage. Not preserving web content would leave a considerable gap in the Belgian historical record. To tackle this challenge, web preservation needs to be addressed on the national level as a cultural and historical necessity, which is why the PROMISE research project (2017–2019) was initiated. As Federal Scientific Institutions (FSI) specialised in heritage preservation, the Royal Library of Belgium and the National Archives partnered with the Universities of Ghent and Namur and the university college Bruxelles-Brabant to bring together their expertise in IT, law, information science and digital humanities to study web archiving. The web archiving strategy resulting from this research project is presented in this article comprising the different phases of the web archiving process, the legal framework, a stakeholder analysis and cost calculation for the different web archiving scenarios.